The present invention relates to lampholder. More particularly this invention concerns two-part holder for a high-voltage lamp.
A standard two-part holder for a high-voltage lamp has a core or insert part into which the lamp end is fitted, and an outer part into which the core part is in turn fitted. Appropriate formations interconnect the two parts and connections and terminals are provided to conduct electricity from outside the outer part to contacts on the lamp in the core part.
In one known such lampholder the outer part is provided with an external screwthread for mounting it in a light fixture or for mounting a shade or globe on it. This outer part has on its outer end toward the lamp a pair of diametrally opposite spring hooks that can snap into engagement with opposite shoulders of the core part that is fitted axially into it. Since the outer part is made of plastic, there is typically considerable play between it and the core part which projects considerably from the outer part which engages around only its end portion. The lamp is therefore not solidly mounted, and the electrical connections to it are poorly shielded.
Another known system has an outer part formed as a cup or sleeve from whose walls are cut a pair of diametrally opposite and inwardly projecting tongues. When the core part is inserted into this outer part, the tongues are spread, and once the core part is fully inserted they click into place in front of outwardly directed shoulders on the core to lock it in place. While such a lampholder does hold the insert or core part more solidly, it has radially throughgoing slots around the deflectable retaining tongues, and these slots present a possible shock hazard.
When such a lampholder is designed for use with a halogen lamp that gets very hot, it is necessary to make the lampholder of a highly heat-resistant material. Plastics such as polyphenyl sulfide (PPS) or liquid crystal polymer (LCP), which art stable at temperatures up to 270xc2x0 C., are used, as well as some ceramics. The problem with these materials is that they are quite brittle. Thus the deformation of fitting them together can damage them. Furthermore to remove the core, it is necessary to insert a tool between it and the outer part to pry back the retaining formations, and this can damage both parts. In addition when such lampholders are used with high-voltage lamps, they cannot have any perforations, as for instance made when the core is held in place by integral, cut-out fingers, so that such construction is ruled out or a separate insulation sleeve must be provided.
It is therefore an object of the present invention to provide an improved two-part holder for a high-voltage lamp.
Another object is the provision of such an improved two-part holder for a high-voltage lamp which overcomes the above-given disadvantages, that is which is of simple durable construction, and that is completely closed for use with a high-voltage lamp.
A lampholder has according to the invention an outer sleeve centered on an axis and having a radially inwardly projecting lug having an axially inwardly directed end face and an inner core adapted to fit with a lamp, fittable inside the sleeve, and formed with an axially inwardly directed face axially alignable and engageable with the outer-sleeve end face on rotation of the core in the sleeve in a predetermined sense in a fully inserted position of the inner core in the sleeve. Interengageable retaining formations on the core and on the sleeve inhibit rotation of the core in the sleeve opposite to the predetermined sense when the faces are axially aligned with and engage each other.
Thus the core and sleeve are connected together by an integral bayonet joint. Such a connection does not rely on deformation of the parts, made of a high-temperature-resistant plastic for instance, so that damage to them is unlikely. Such a bayonet joint can however resist considerable separation forces so that when the lamp must be replaced, it can simply be pulled out of the core and a new one inserted, with no worry of the core stripping out of the sleeve. What is more, fitting them together is a relatively simple task involving axially sliding the insert into the sleeve, then rotating it through a small angle until the two faces are aligned and the retaining formations fit together.
The lug according to the invention is recessed in the sleeve and the sleeve is radially imperforate. Thus the lampholder according to the invention can be used with a high-voltage lamp, for instance a halogen bulb. There are no punched-out retaining tongues that could create a shock risk.
The sleeve in accordance with the invention is further formed adjacent the inwardly directed face with an axially extending and radially outwardly open groove along which the lug can move axially on axial inward insertion of the core into the sleeve. Furthermore the interengageable retaining formations include a radially inwardly projecting formation on the sleeve and a radially outwardly projecting formations on the core. Each of the formations has a edge face extending in a plane generally parallel to and radial of the axis and an opposite angled cam surface. The cam surfaces allow the formations to pass each other on rotation in the predetermined installing direction, while the edge faces prevent opposite rotation. The formation of the core is immediately adjacent the groove, in fact it defines one edge of the groove.
The sleeve according to the invention is formed with an external screwthread, preferably measuring 20.8 mmxc3x972 mm. Such a screwthread is standard in low-volt lamps, so that the lampholder according to the invention can accept standard gloves and fit in standard installations.